Size 9×12 9×12 9×12 9×12 10×13 10×13 6×9. 9×12 Durable Envelopes: catalog envelopes are made of sturdy 28 lb brown kraft paper, featuring a robust self-seal closure. Self-Sealing Envelopes: 9×12 Manila envelopes are designed with ultra-strong self-adhesive tape.